Question

explain need of modulation

Answer 1

Hey there!

Answer:


The frequency of audio signal is 20 Hz to 20, 000 Hz. Due to low frequency audio signal can not be transmitted directly into space by converting into electric waves because ;



( 1 ). For transmission and reception, height of antenna must be $\lambda$/4.

For example:

frequency = 15 kHz

We know;

L = $\lambda$/4

$\lambda$ = c/v

Where c is speed of light = 3 × $10^{8}$

and v is frequency = 15kHz ( Given ) = 15 × $10^{3}$m

Using value of $\lambda$

We get;

L = $\dfrac{3 × 10^{8}}{4 × 15 × 10^{3}}$

L = 5000m

It is not possible to get antenna of this height.

Therefore;

frequency = 1 MHz = $10^{6}$m

L = $\dfrac{3 × 10^{8}}{4 × 10^{6}}$

L = 75 m.

which is possible.



( 2 ). Various voice frequency signals mixed up hence it become difficult to distinguish these signals at the recieving antenna.



( 3 ). P $\propto$ $\dfrac{1}{\lambda^{2}}$

Power radiated is more for shorter wavelength. so power should be high.



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